The coordinated multi point technology can be used for enlarging a cell coverage area of the high data rate and improving throughput of the cell-edge user, thereby improving the system throughput. At present, this technology has been used in a Long Term Evolution-Advanced (LTE-Advanced) system so as to improve the overall system performance.
A basic concept of the CoMP is multiple transmission points at different geographical locations coordinating to serve one or more than one user. The CoMP downlink transmission technology can be divided into two cases: Coordinated Scheduling (CS) and Joint Transmission (JT). Wherein, the coordinated scheduling refers to multiple transmission points within a coordinated set participating in the coordinated scheduling, a scheduling result is only one transmission point sending downlink data of the User Equipment (UE) on the same time-frequency resource; and the joint transmission refers to multiple points performing coordination to transmit downlink data of one UE simultaneously.
In the LTE system, the UE calculates a Channel Quality Indicator (CQI) based on a certain time domain observed result and frequency domain observed result, and feed back the CQI to a Base Station (BS) through an uplink subframe, and the BS uses a corresponding modulation and coding scheme according to a CQI value fed back by the UE. Generally, a range of the CQI value is 0˜15, each of CQI values 1˜15 corresponds to one modulation and coding scheme, in a channel condition responded by a reference signal corresponding to the CQI measurement, the corresponding modulation and coding scheme is adopted to perform Physical Downlink Shared Channel (PDSCH) transmission, and a received block error rate should not exceed 0.1. When this condition cannot be satisfied, a CQI value is 0. The CQI values from low to high respectively represent modulation and coding rates of the data from low to high namely transmission efficiencies of the data from low to high. Therefore, if a CQI value is higher, it indicates that a channel transmission condition is better, and data with a higher modulation and coding rate can be transmitted.
In the Rel-8/Rel-9 LTE system, only one BS serves one UE, thus all signals of other BSs are interference signals to the UE. The UE performs Per-Cell CQI calculation and feedback according to this assumption. After the CoMP mechanism is introduced, multiple BSs simultaneously send data of one UE, if the UE still performs CQI calculation according to the Rel-8/Rel-9 way, generally effective signals from a coordinated cell will be taken as interference signals to be processed, a lower CQI calculated value is caused, and the BS can only adopt a more conservative modulation and coding scheme. Even though the modulation and coding scheme also can be adjusted through Open-Loop Link Adaption (OLLA) in the LTE, the workload of the OLLA will be certainly increased, and the oscillation during an Adaptive Modulation and Coding (AMC) process will be aggravated.